1. Field of the Invention
This invention relates to the field of hydraulic circuits for automatic transmission control.
2. Description of the Prior Art
A hydrokinetic torque converter, which forms a hydrokinetic torque flow path from the engine crankshaft to the input elements of a gear ring of an automatic transmission, includes a turbine and an impeller arranged in a toroidal fluid flow circuit. It includes also a friction bypass clutch adapted to connect the impeller to the turbine to establish a mechanical torque flow path in parallel with respect to the hydrokinetic torque flow path of the torque converter.
The hydrokinetic torque converter of our invention includes a bypass clutch controlled by an hydraulic valve system. The bypass clutch has features that are common to the control system described in U.S. Pat. No. 5,029,087, and the hydrokinetic torque converter control system of U.S. Pat. No. 5,303,616. These patents are assigned to the assignee of our present invention. The '087 patent describes a torque converter control system having a lock-up clutch for establishing a controlled mechanical torque flow path between the engine and the transmission gearing and for modifying the bypass clutch capacity during shift intervals. That patent discloses an electronic control strategy for effecting a control slip in a torque converter bypass clutch, whereby the bypass clutch is actuated by modulated converter clutch solenoid pressure from a clutch solenoid valve to effect varying clutch capacity so that the resulting control slip results in an actual slip that approaches a target slip determined by the operating parameters of the driveline.
The '616 patent describes a torque converter control system having a lock-up clutch for establishing a controlled mechanical torque flow path between the engine and transmission gearing and for modifying the bypass clutch capacity during gearshift intervals.
The system of this invention permits two fixed displacement pumps to operate in several distinct modes: combined delivery, secondary pump supercharged, and clutch pump boosted. A feature of this system is the supercharge circuit that regenerates waste hydraulic power to raise the inlet pressure of the secondary pump above atmospheric pressure.
In a conventional hydraulic circuit for an automatic transmission, the fluid from the torque converter and cooler provides most of the fluid to the lubrication system because the converter, cooler and lubrication system are arranged in series. In some conventional hydraulic systems, one or more separate circuits are fed from a source of line pressure so that during periods when pump flow demand is high, such as when torque converter and cooler flow is throttled or dead-headed, not all of the fluid directed to the lubrication system is throttled or closed.